Tar pits' microfossils stir big interest from Page museum scientists

Louis Sahagun

Perhaps in pursuit of prey, a senior saber-tooth cat with chronic arthritis and damaged teeth fell into the death trap now known as the La Brea tar pits and died, attracting swarms of scavenging insects and rodents.

Eventually, the rotting carcass and its parasites were entombed in the sticky mire, continuing the cycle of death in a site renowned as the world's richest deposit of late Ice Age fossils.

This is only part of the story emerging from remnants of the big cat and other animals excavated by Page Museum paleontologists at the La Brea tar pits. Between the bones and inside the skulls are troves of microfossils — beetle wings, ant legs, chips of tooth enamel, twigs — that are opening new windows onto the ecology of prehistoric Los Angeles at a time when the climate was starting to heat up.

Although the museum is best known for its crowd-pleasing mastodons, sloths, bison, dire wolves and saber-tooth cat skeletons, much of the emphasis of its current research has shifted toward the study of tiny fossilized organisms.

Once tossed aside as inconsequential, microfossils have come to be regarded as critical to reconstructing the ecology and climatic conditions at the end of the Pleistocene Epoch, between 10,000 and 50,000 years ago, and better understanding current climate change.

"For decades we collected and presented statue-like examples of the mega-fauna of the past," John M. Harris, chief curator of vertebrate studies at the Natural History Museum of Los Angeles County, said. "Now, we're attempting to preserve a whole prehistoric ecosystem and chronicle how it changed over time."

It's all grist for discussion and debate during an international gathering of paleontologists starting Tuesday and hosted by the museum on its 100th anniversary. Lectures at the annual Society of Vertebrate Paleontology conference will focus on topics ranging from what insect-damaged fossils reveal about the Ice Age to advances in technology for dating and analyzing chemical composition with greater precision than ever.

"These tiny bits and pieces may not look exciting, but they have become the coolest things on this planet," Luis Chiappe, vice president of research and collections at the Natural History Museum, said. "The menageries of insects, lizards and snakes emerging from our excavations are telling stories you can't get from a mammoth skeleton alone."

Tiny holes in bison bones may indicate the presence of specific species of insect larvae on decomposing carcasses at particular stages of decomposition and under certain climatic conditions. Weevils and wood-boring beetles leave characteristic engravings on wood.

Grooves on the toe bones of a horse show that its carcass had been sticking out above the surface of a tar pool for several weeks and was being defleshed by a species of beetle that emerges only in warm weather.

Then there's the recently unearthed skull of "Gimli," the aging saber-tooth cat that died in a tar pit. The football-sized fossil contained thousands of valuable fragments, including one prized by Shelley Cox, Page laboratory supervisor: a thorax of an ant no bigger than a grain of salt.

"Next to Gimli we found skeletal remains of at least 18 horned lizards, which eat ants," Cox said, peering at the fragments of lizard bones under a dissecting microscope. "So we were able to make a connection that sharpens our knowledge of a moment in time and place."

Among those attending this week's event is John Southon, a researcher at UC Irvine's school of physical sciences, who has been collaborating with the Page on the dating and isotopic analysis of fossils from Project 23: — 23 blocks of sediment extracted from the ground during construction of the nearby Los Angeles County Museum of Art parking lot.

"The ultimate aim is to understand how the whole ecosystem responded to change in the past — what thrived, what went extinct, when and why," Southon said. "The answers can help us make more intelligent predictions about our own future."

In the meantime, Page Museum officials are developing plans to revamp their exhibits to include displays of the diminutive neighbors of the giants that reigned in the Los Angeles area, along with explanations of their role in the region's prehistoric rhythms of life.

"The exhibits on display at the Page Museum haven't changed much since we opened in 1977," Harris said. "But over the next five years, we're going to change all that. We'll have the 'wow' of gigantic skeletons, as well the little things that lived beneath them."